Time since last vaccine dose in PCR-positive and PCR-negative children with suspected pertussis to monitor pertussis vaccine effectiveness.

We evaluated whether the results of diagnostic polymerase chain reaction (PCR) testing combined with time since last vaccine dose could be used to monitor the effectiveness of acellular pertussis vaccines. In 258 consecutive nasopharyngeal swabs from children and adolescents with typical pertussis symptoms, 80 were positive and 178 were negative in PCR for Bordetella pertussis DNA (IS 481). Time since last vaccine dose was available for 152 patients, of which 120 were fully immunised. Among the fully vaccinated patients, the median age of 41 PCR-positive patients was 8.4 years (range 0.9-12.3) and that of 79 PCR-negative cases was 3.3 years (range 0.4-14.1) (p < 0.01). The median time since last pertussis vaccine dose was 6.05 years [95 % confidence interval (CI): 0.5-10.9] in PCR-positive cases and 2.22 years (95 % CI: 0.04-9.23) in PCR-negative cases (p < 0.001). The use of diagnostic PCR results from pertussis cases together with time since last vaccine dose permits estimates of the duration of protection after vaccination with acellular pertussis vaccines that are in keeping with more complex studies.